• Journal of Communications and Networks
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• v.3 no.4
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• pp.383-395
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• 2001

Recent measurement and simulation studies have revealed that wide area network traffic displays complex statistical characteristics-possibly multifractal scaling-on fine timescales, in addition to the well-known properly of self-similar scaling on coarser timescales. In this paper we investigate the performance and network engineering significance of these fine timescale features using measured TCP anti MPEG2 video traces, queueing simulations and analytical arguments. We demonstrate that the fine timescale features can affect performance substantially at low and intermediate utilizations, while the longer timescale self-similarity is important at intermediate and high utilizations. We relate the fine timescale structure in the measured TCP traces to flow controls, and show that UDP traffic-which is not flow controlled-lacks such fine timescale structure. Likewise we relate the fine timescale structure in video MPEG2 traces to sub-frame encoding. We show that it is possibly to construct a relatively parsimonious multi-fractal cascade model of fine timescale features that matches the queueing performance of both the TCP and video traces. We outline an analytical method ta estimate performance for traffic that is self-similar on coarse timescales and multi-fractal on fine timescales, and show that the engineering problem of setting safe operating points for planning or admission controls can be significantly influenced by fine timescale fluctuations in network traffic. The work reported here can be used to model the relevant characteristics of wide area traffic across a full range of engineering timescales, and can be the basis of more accurate network performance analysis and engineering.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11A
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• pp.1872-1879
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• 2001

As multiview video applications become more popular, correspondence problem for stereo image matching plays an important role in expanding view points. Thus, we propose an efficient dense disparity estimation algorithm considering features of each image pair of multiview image sets. Main concepts of the proposed algorithm are based on the region-dividing-bidirectional-pixel-matching method. This algorithm makes matching process efficient and keeps the reliability of the estimated disparities. Other improvement have obtained by proposed cost function, matching window expanding technique, disparity regularization, and disparity assignment in ambiguous region. These techniques make disparities more stable by removing false disparities and ambiguous regions. The estimated disparities are used to synthesize intermediate views of multiview images. Computer simulation demonstrates the excellence of the proposed algorithm in both subjective and objective evaluations. In addition, processing time is reduced as well.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.355-363
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• 2013

Panel methods are essential tools for analyzing a fluid-flow problem around complex three dimensional bodies, but they lack ability to solve viscous effects. On the other hand, CFD methods are considered as powerful tools for analyzing fluid-flow characteristics including viscosity. However, they also have short falls, requiring more computing time and showing different results depending on the selection of turbulence models and grid systems. In this paper a hybrid scheme combining a panel method and a CFD method is suggested. The scheme adopts a panel method for far-field solution where viscous effects are negligible and a CFD method for the solution of RANS equations in near-field where viscous effects are relatively strong. The intermediate region between the far-field and near-field is introduced where the calculated field point velocities by the panel method are given as boundary velocities for the CFD method. To verify the scheme, calculated results, by a panel method, a CFD method and the hybrid scheme, for a two dimensional foil section are compared. The suggested hybrid scheme gives reasonable results, while computation time and memory can be dramatically reduced. By using the hybrid scheme efforts can be concentrated for the local flow near the leading and trailing edges, by providing more dense grid system, where detailed flow characteristics are required.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.3
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• pp.513-518
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• 2016

This paper presents a fast 3D mesh generation method using projection for line laser-based 3D scanners. The well-known method for 3D mesh generation utilizes convex hulls for 4D vertices that is converted from the input 3D vertices. This 3D mesh generation for a large set of vertices requires a lot of time. To overcome this problem, the proposed method takes (${\theta}-y$) 2D depth map into account. The 2D depth map is a projection version of 3D data with a form of (${\theta}$, y, z) which are intermediately acquired by line laser-based 3D scanners. Thus, our 2D-based method is a very fast 3D mesh generation method. To evaluate our method, we conduct experiments with intermediate 3D vertex data from line-laser scanners. Experimental results show that the proposed method is superior to the existing method in terms of mesh generation speed.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.181-186
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• 2006

In this paper, generation mechanisms of ocean freak waves are briefly introduced in the context of wave-current interaction phenomena. The present model of the fluid motion is based on the Navier-Stokes equations incorporating velocity-pressure formulation because of need to model the nonlinear wave interaction with spatially non-uniform current field. In order to deal with the free surface motion, an Arbitrary Lagrangian-Eulerian (ALE) description is adopted. As an accurate and efficient numerical tool, the spectral element method is presented with general features and specific treatment for the wave-current interaction problem. As an intermediate stage of development, solution procedure and characteristics aspects of the present modeling and numerical method are addressed in detail, and preliminary numerical results prove its accuracy and convergence.

• 한국HCI학회:학술대회논문집
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• 2009.02a
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• pp.685-689
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• 2009

Evolutionary Computation is not only widely used in optimization and machine learning, but also being applied in creating novel structures and entities. This paper proposes evolutionary topic maps that can suggest new and creative knowledge not easily producible by humans. Interactive evolutionary computation method is applied into topic maps in order to accept human evaluation on feasibility of intermediate topic maps. Evolutionary topic maps are creativity support tools, helping users to encounter new and creative knowledge. Further work can greatly improve the system by providing more operations, preventing over-convergence, and overcoming user fatigue problem by providing more intuitive user interface, better visualization, and interpolation mechanisms.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.825-829
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• 2005

This paper presents an approach for designing a fuzzy logic-based adaptive SVC damping In controller for damping low frequency power oscillations. Power systems are often subject to low Frequency electro-mechanical oscillations resulting from electrical disturbances. Generally, power system stabilizers are designed to provide damping against this kind of oscillations. Another means to achieve damping is to design supplementary damping controllers that are equipped with SVC. Various approaches are available for designing such controllers, many of which are based on the concepts of damping torque and others which treat the damping controller design as a generic control problem and apply various control theories on it. In our proposed approach, linear optimal controllers are designed and then a fuzzy logic tuning mechanism is constructed to generate a single control signal. The controller uses the system operating condition and a fuzzy logic signal tuner to blend the control signals generated by two linear controllers, which are designed using an optimal control method. First, we design damping controllers for the two extreme conditions; the control action for intermediate conditions is determined by the fuzzy logic tuner. The more the operating condition belongs to one of the two fuzzy sets, the stronger the contribution of the control signal from that set in the output signal. Simulation studies done on a one-machine infinite-bus and a four-machine two-area test system, show that the proposed fuzzy adaptive damping SVC controller effectively enhances the damping of low frequency oscillations.

• Asian Pacific Journal of Cancer Prevention
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• v.17 no.3
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• pp.1589-1593
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• 2016

Opisthorchis viverrini (OV) liver flukes are common parasites found in central and southern Laos and constitute a major public health problem in the country. Laos people continue to have the habit of extensively consuming raw or half-cooked fish which are intermediate hosts. This study aimed to determine the prevalence and factors associated with OV infection in the population of Thakek district, Khammouane Province. This cross-sectional analytic study covered 237 subjects who filled out structured questionnaires. Fecal examination for OV infection was performed by Kato's thick smear method. Data analysis was carried out using STATA Version 10.0. Multiple logistic regression was applied. The results showed that the infection rate of OV was 54.8%. Factors associated with OV infections were gender, a habit of defecation in fields and raw fish (goi bplaa dip) consumption. Opisthorchiasis and associated cholangiocarcinoma development thus appear to remain as important concerns in Laos.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1821-1832
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• 2016

This study presents a strategy using the synchronized output regulation method (SOR) for controlling inverters operating in stand-alone and grid-connected modes. From the view point of networked dynamic systems, SOR involves nodes with outputs that are synchronized but also display a desirable wave shape. Under the SOR strategy, the inverter and grid are treated as two nodes that comprise a simple network. These two nodes work independently under the stand-alone mode. An intermediate mode, here is named the synchronization mode, is emphasized because the transition from the stand-alone mode to the grid-connected mode can be dealt as a standard SOR problem. In the grid-connected mode, the inverter operates in an independent way, in which the voltage reference changes for generalized synchronization where its output current satisfies the required power injection. Such a relatively independent design leads to a seamless transfer between operation modes. The closed-loop system is analyzed in the state space on the basis of the output regulation theory, which improves the robustness of the design. Simulations and experiments are performed to verify the proposed control strategy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.1
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• pp.80-89
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• 1992

This paper presents algorithms which are region labeling and data structure of a boundary segmentation as image intermediate description process. In the method, the algorithms are region labeling, boundary segmentation, line and curve fitting and extracting data structure of each segment. As a result, a data structure of image is described by a set of region number, segment number, line or curve, starting point and end point of each segment and coefficient of line or curve. These data structures would serve for higher level processing as object recognition. For example we will use this data structure to solve the correspondence problem of stereoscopic image information. And we verified these algorithms through the image reconstruction of data structure.